Field of the Invention
This invention generally relates to optical-mechanical apparatus and more specifically to opto-mechanical apparatus having a small cross section that includes a housing and an optical element.
Description of Related Art
A significant effort has been made and continues to be made toward the development of opto-mechanical apparatus with increasingly smaller transverse cross sections. This is particularly true in the medical field where diagnosis and related treatment regimens for endoscopic devices is expanding with the introduction of smaller, reliable and reasonably priced opto-mechanical apparatus. Presently there are efforts underway to produce cylindrical lenses that have diameters less than 2 mm and even in the range of 1 mm or less.
Such small opto-mechanical apparatus generally has several major components. For purposes of describing this invention there are two such components, namely: (1) an optical element that may comprise a lens, an optical window or combination of one or more of each and (2) a housing that supports each optical element on an optical axis. As the demand for smaller and smaller diameter lenses continues to increase, new problems have emerged that can detract from the efficacy of such new apparatus. First, the housing can overlie the imaging surface of an optical element and thereby reduce the optical field of view for that apparatus. Second, the method by which the optical device is retained in the housing can fail during use. Third, such apparatus must be constructed so that its exterior surface is smooth for easy cleaning.
FIG. 1 depicts a prior art opto-mechanical assembly 10 that maximizes the field of view, but includes a retaining structure that is subject to failure. The assembly 10 includes a conventional biconvex lens 11 as an optical element. A housing 12 has a distal end 13 and aligns the lens 11 along an optical axis 14. The right side of the assembly 10 in FIG. 1 extends to a proximal end (not shown, but known in the art). The housing 12 also contains an integral, radially inwardly extending band 15 that forms a shoulder or seat 16 against which the proximal side of the lens 11 seats. Adhesive material 17 fills gaps 18 and 19 between the outer periphery of the lens 11 and the coextensive spaced inner surfaces of the housing 12. When completed, the distal ends of the lens 11 and the housing 12 are flush and create a smooth surface to facilitate cleaning and reduce contamination during use by eliminating any crevices or the like in the apparatus. The retention of the lens 11 within the housing 12 of this apparatus 10, however, depends solely upon the adhesion that exists between the adhesive material 17 and the adjacent surfaces of the lens 11 and housing 12. Such adhesion, in turn, depends upon the contact area for the adhesive material that, in the configuration of FIG. 1, is proportional to lens diameter and length. Adhesion is also dependent upon the surface roughness and the materials that contact the adhesive material.
Such opto-mechanical assemblies can be subjected to environmental conditions that create forces on the bonds produced by the adhesive material. Such forces can be generated by accident, as by exposing the bond to a mechanical shock, by dropping the assembly, or by wide temperature or other environmental factors that produce differential expansions of the lens 11 and the housing 15. If such a force is large enough to exceed the adhesion characteristics of the adhesive material 17, the adhesive material could decouple from the lens 11 and/or housing 12 whereupon the bi-convex lens 11 could shift distally and become unstable axially or even completely separate from the housing 12. In either event, the opto-mechanical assembly 10 would require factory repair or even replacement. Also, if the lens 11 were to separate from the housing 12, negative consequences for the procedure being performed with the assembly could result. Thus, as will be apparent to those skilled in the art, the specific opto-mechanical assembly in FIG. 1 provides a maximum field of view and smooth distal surface, but a less than optimal resistance to shock and other environmental factors.
FIGS. 2A and 2B depict variations of opto-mechanical assemblies that utilize mechanical retention structures that, as will become apparent, strengthen the retention characteristics, but also decrease field of view and result in non-smooth surfaces. FIG. 2A discloses an opto-mechanical assembly 20 with a housing 21 and a plano-convex lens 22. The opto-mechanical assembly 20 has an optical axis 23. In this variation, an angular radially inwardly extending lip 24 forms a positioning stop 25 that blocks any distal shift of the lens 22. During manufacture, the lens 22 is inserted from the proximal end of housing 21 until it reaches the shoulder 25. Thereafter, a mechanical element such as a lens spacer 26 is inserted into the housing 21 from the proximal end. Other means lock the lens spacer 26 into its axial position so the lens spacer 26 blocks any proximal shift of the lens 22.
In the other variation of FIG. 2B an opto-mechanical assembly 30 includes a housing 31 with a bi-convex lens 32 extending along an optical axis 33. The lens 32 is loaded into the housing from the distal end 34 until it contacts a shoulder on a positioning band 35 that is integral with the housing 31 thereby to block any further proximal lens shift. At a distal end 34, the housing 31 receives a retainer element 36 that includes an internally threaded extension 37 that mates with an axially distally extending extension 38 from the housing 31. A radially inwardly extending lip 39 engages the lens 32 and prevents any distal lens shift of the lens 32.
Each of these embodiments provides a structure that blocks any proximal or distal shift and that can withstand mechanical shock, and other environmental conditions that generate forces between the optical and mechanical elements. However, the lip 24 in FIG. 2A and the lip 39 in FIG. 2B limit the field of view because they overlap the distal ends of the lenses 22 and 32 respectively, thereby reducing their clear apertures and because they extend axially beyond the distal lens surface. In addition, as these retaining structures extend beyond the distal surface of their respective lenses, the distal surface of the lens 22 in FIG. 2A and the distal surface of the lens 32 in FIG. 2B are not flush with the distal most surfaces of the housings 21 and 32, respectively. Cleaning of the exterior surface, which is not smooth, is therefore more difficult due to the interior angles. These non-smooth surfaces also act as locations for buildup of contamination during use. For an opto-mechanical assembly of a given size, the cost of adding in separate locking elements and fastening them in a secure manner increases the expense of manufacture. Moreover, as the apparatus size decreases, manufacturing complexity and concomitant costs increase. In fact for lens assemblies that are very small, for example less than 2 mm, the cost of adopting such a construction technique can become commercially and technically prohibitive.
What is needed is an opto-mechanical assembly that is adapted for including small optical elements in a small housing that optimizes field of view, that optimizes the mechanical structure for reliable mechanical containment and that facilitates cleaning. What also is needed is such an apparatus that is commercially and technically feasible.